The provided code models the Large conductance calcium-activated potassium (BK) channels, often referred to as BK channels or mslo channels. These channels play a pivotal role in regulating neuronal excitability and function by integrating both membrane voltage and intracellular calcium signals. Here are the key biological aspects captured by this model:
Ionic Species: The model describes a channel that selectively allows potassium ions (K+) to flow through it. This is implemented in the model by using the USEION k
mechanism to read and write the reversal potential (ek
) and current (ik
).
Calcium Activation: The channel is activated by intracellular calcium concentrations (cai
and ca2i
). These calcium ions bind to the channel, altering its open probabilities and activating it. The USEION ca
and USEION ca2
keywords with READ cai
and READ ca2i
allow the channel's activity to be dependent on these internal calcium levels.
State Representation: The channel can exist in multiple states, represented by closed states (C0
to C4
) and open states (O0
to O4
), indicating the channel's ability to transition from being closed to open as it binds calcium ions.
Transition Rates: The transitions between these states are governed by transition rates (c01
, c12
, etc.), which depend on calcium concentration and membrane voltage. These rates are calculated to capture the kinetics of calcium binding and unbinding, as well as the channel transitioning between different conformational states.
qt
, calculated as q10^((celsius-23)/10)
, which adapts the reaction rates based on experimental temperature conditions, thereby aligning the model to the biological environment in which these channels operate.Qo
and Qc
. These variables affect the transition rates and describe how the channel's gating is influenced by membrane potential. This aspect is responsible for translating changes in membrane voltage into altered gating kinetics.In summary, this code provides a mathematical representation of the calcium- and voltage-sensitive kinetics of large conductance BK channels, crucial for maintaining the excitability and firing patterns of neurons, especially in the context of Purkinje cells within the cerebellum.